Comparative surfacing studies of sputtered and thermal annealed ZnO films wet etched with NH4Cl and acidic etchants

The wet etchings of as-grown and thermal annealed ZnO films were carried out by using NH4Cl and acidic etchants respectively. The lateral profiles and side faces of the etched ZnO samples were exhibited by profiler and SEM measurements. NH4Cl etchant can avoid W-like lateral profile and eave-like slope at the side face of the etched ZnO patterns for both as-grown and post-annealed ZnO samples. The etching rate has been compared between NH4Cl etchant and acidic etchants for both as-grown and post-annealed ZnO samples. NH4Cl etchant can maintain slower etching rate with higher NH4Cl concentration. The thermal annealing procedure can be helpful to achieving uniform etching surface, and the etching rates of the annealed ZnO samples are even slower, which can be explained by the better crystallinity and lower density of oxygen vacancy.